Abstract The maximum burial depth and thermal maturity of a hydrocarbon source rock controls the generation of petroleum, and data on rock maturity are necessary for an understanding of a petroleum system. Rock-Eval pyrolysis is an established method to assess the hydrocarbon generation potential, the type of organic matter (kerogen type), but also the thermal maturity of hydrocarbon source rocks. Data on the thermal maturity of source rocks and/or of the generated hydrocarbons are, however, often lacking either, because (i) the source rock itself is not available or (ii) today’s maturities cannot be directly linked to a generated petroleum, because petroleum generation and expulsion may have taken place at an earlier and less mature stage of the source rock. Indirect records of source rock maturities can be inferred from the physical properties of petroleum (e.g, API gravity), from biomarker abundances or from individual hydrocarbon ratios (including biomarkers). Using an adapted direct Rock-Eval pyrolysis approach for petroleum samples we present data from oils from the BGR petroleum archive. We distinguish between two hydrocarbon release-stages during Rock-Eval pyrolysis of which the first represents a vaporizable mid-molecular (S1oil) fraction ( n-C40) and the second (S2oil) fraction (> 400 °C; > n-C40) most likely represents a residual higher-molecular weight petroleum fraction generating hydrocarbons by pyrolytic destruction. Using this program, we calculate an “Oil Composition Index” (OCI). Unless processes like biodegradation, evaporation or migration can affect OCI values, in a relatively well known petroleum system without major influences from these processes (the Gifhorn Trough in the Lower Saxony Basin [LSB] in Northern Germany), our data indicate that maturity of the source rock during expulsion is key for OCI. Application of Rock-Eval on a large set of oils from the entire LSB demonstrates that OCI values further hold information on the kerogen-type of the source rock (Wealden vs. Posidonia shales).

中文翻译：

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石油直接 Rock-Eval 热解的地球化学意义

摘要 烃源岩的最大埋藏深度和热成熟度控制着石油的生成，而岩石成熟度数据是了解油气系统的必要条件。Rock-Eval 热解是评估生烃潜力、有机质类型（干酪根类型）以及烃源岩热成熟度的成熟方法。然而，关于烃源岩和/或生成的碳氢化合物的热成熟度数据往往缺乏，因为 (i) 烃源岩本身不可用或 (ii) 今天的成熟度不能直接与生成的石油相关联，因为石油的生成和排出可能发生在烃源岩较早和不太成熟的阶段。烃源岩成熟度的间接记录可以从石油的物理特性（例如 API 重力）、生物标志物丰度或单个碳氢化合物比率（包括生物标志物）中推断出来。使用适用于石油样品的直接 Rock-Eval 热解方法，我们提供了来自 BGR 石油档案的石油数据。我们区分 Rock-Eval 热解过程中的两个碳氢化合物释放阶段，其中第一个代表可汽化的中分子 (S1oil) 馏分 (n-C40) 和第二个 (S2oil) 馏分（> 400 °C；> n-C40）最有可能代表通过热解破坏产生碳氢化合物的残余高分子量石油馏分。使用该程序，我们计算“石油成分指数”（OCI）。除非生物降解、蒸发或迁移等过程会影响 OCI 值，在一个相对知名的石油系统中，不受这些过程的重大影响（德国北部下萨克森盆地 [LSB] 的 Gifhorn 海槽），我们的数据表明，在排出过程中烃源岩的成熟度是 OCI 的关键。Rock-Eval 对来自整个 LSB 的大量石油的应用表明，OCI 值进一步掌握了有关烃源岩干酪根类型的信息（Wealden 与 Posidonia 页岩）。